5 Shortly after, his ideas were presented to the Russian Physico-chemical Society. They were read by Professor Menschutkin because Mendeleev was ill. His ideas were then published in the main German chemistry periodical of the time, Zeitschrift fϋr Chemie.The world’s first view of Mendeleev’s Periodic Table – an extract from Zeitschrift fϋr Chemie, Click here for a translation

8 Periodic trends Vary systemically across a period (horizontally)down a group (vertically)

9 Atomic radiiBased on probability of electron cloud, therefore, defined by how closely an atom lies to a neighboring atomDECREASES to the right across a periodDue to larger nuclear attractionINCREASES down a groupDue to more “layers” of electrons

11 Ionic RadiiIons (charged atoms) form when electrons are gained or lost….(the number of protons and electrons don’t match!)DECREASES to the right across a period (in two phases)INCREASES down a group

13 Ionization EnergyDefined as “amount of energy required to remove an electron from a gaseous atom”1st ionization energy2nd ionization energyEtc.Think of this as the atom’s ability to hold onto its valence electron!INCREASES across a periodHarder to remove e-Positive energy means “harder”DECREASES down a groupEasier to remove e-More negative energy means “easier” or “more stable”

15 Octet RuleAtoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electronsNote chemical stability of noble gasesPredicts ionic charge of main block elementsCATIONS—positively charged ions (lost e-)ANIONS—negatively charged ions (gained e-)

16 Electron AffinityEnergy associated with adding an electron to an atom’s electron cloud---think of the opposite of Ionization Energy…but same effect!INCREASES (but the energy gets more negative = means “more stable”) across periodDECREASES (but the energy value gets more positive = means “more difficult”) down groupTherefore, a great idea!....

17 ElectronegativityIndication of the relative ability of the atom to attract electrons in a chemical bondThink of this quantity as how strongly an atom might want to gain an electron.Arbitrary rating scaled to 4.0…..Most electronegative element is fluorine with 3.98INCREASES across a periodDECREASES down a group